1. Field of the Invention
The present invention relates to an apparatus, a method for performing a scan procedure, and a mobile station comprising the same. More specifically, the present invention relates to a mobile station, a method for performing a scan procedure according to an orthogonal frequency division multiple access (OFDMA) signal, and a mobile station comprising the same.
2. Descriptions of the Related Art
For OFDMA application over a wireless channel, a mobile station (MS) has to make a connection with a base station (BS) in order to be served. The BS which serves the MS is called the serving BS (SBS) and the other BSs that the MS is able to listen to are called the neighboring BSs (NBSs).
There are some occasions that an MS has to determine whether to switch from its current SBS to one of its NBSs. One of the occasions is when the MS detects that the connection with its SBS is getting worse, and the MS performs a scan procedure to find one of the NBSs to switch to. Another occasion is that the MS keeps monitoring the status of all the NBSs, i.e. the MS periodically performs the scan procedure, and then determines wither to switch from the current SBS to one of its NBSs according to the result of the scan procedure.
A scan procedure is used by an MS to determine whether to switch the SBS, which measures the quality of the physical layer connection with each of the NBSs. The most important factor representing the connection quality is the channel interference and noise ratio (CINR). To measure the CINR of each NBS, an MS must have the identity of the targeting NBS, wherein the identity of the NBS is given by a SBS. When the OFDMA application conforms to the WiMAX standard, the identity is the parameter CELL_ID defined in the WiMAX standard.
A conventional system for performing a scan procedure utilizes one FFT input buffer, thus the data transmission is often temporary suspended during the transmission. The conventional system may not be able to continue the data transmission until the scan procedure has been done. Thus, the performance of the conventional system is degraded while considering the fact of the delay of the scan procedure.
Please refer to FIG. 1 for better understanding. FIG. 1 illustrates a timing diagram of the conventional system, wherein the time periods 18a, 18c correspond to downlink subframes, the time periods 18b, 18d correspond to uplink subframes, signal BW0 indicates the buffer read of a single FFT buffer, signal BR0 indicates buffer write of the single FFT buffer, signal PP0 indicates the signal of the post-FFT processing, signal CINRM0 indicates the signal of the CINR measurement, and signal FFTC0 indicates the signal of the FFT.
It is noted that the generations of the refined frame boundaries and the CINR values for NBSs happen at the beginning of each downlink sub-frame, which is shown by the toggles of the signals BR0, BW0, PP0, CINRM0, FFTC0 at the beginning of the downlink subframe 18a, 18c. After the generations of the refined frame boundaries and the calculations of the CINRs for NBSs, the conventional system continues to transmit data. From FIG. 1, it is shown that the single FFT buffer, the post-FFT processing, and the CINR measurement are not able to perform effective post-processing during the period correspond to uplink subframe 18b, 18d. 
Form the viewpoint of the hardware, the scan procedure is no different from a normal receive, so no extra hardware is required. However, before starting the scan procedure, the convention system has to request a period to its SBS, since it will lose track of the SBS during the scan procedure. That is, the data transmission is delayed by the scan procedure. Thus, the request/grant procedure for the scan procedure will downgrade the network efficiency.
Other conventional systems are to duplicate CINR measurement for measuring CINR values of different NBSs. The post-FFT processing does not need to generate a refined frame boundary for each NBS. Each of the CINR measurement are measured of the CINR value of the corresponding NBS based on the frame boundary of the SBS but not the refined frame boundary of the NBS. Therefore, the network efficiency is not downgraded when this scan procedure is applied. Regarding to this system, the quality of the CINR measurement suffers from the frame boundary mismatch, especially when it is a large delay spread channel. Moreover, this system raises the cost for utilizing extra CINR measurement modules.
According to the aforementioned description, it is desirable to provide a technique that can perform a scan procedure without downgrading the network efficiency.